1. Field of the Invention
The present invention relates to a method and fan system with a hysteresis character, and more particularly, to a method and fan system that utilizes different temperature threshold values to switch on the fan (or to increase the fan rotational speed) and to switch off the fan (or to decrease the fan rotational speed).
2. Description of the Prior Art
Display efficiency of computer systems are improving in the development of multi-media technology. In general, in order to assure the normal operation of the display card, display card manufacturers tend to set the related settings of the display cards within a safety range before shipping the cards, for example, an operation frequency and an operation voltage of a graphic processing unit tends to be lower than the maximum frequency and the maximum voltage acceptable for the graphic card. In this situation, some users will increase or decrease the operation frequency of the graphic processing unit according to different software to obtain different image processing efficiency. However, the temperature of the display card increases when the graphics-processing unit is processing a complex image calculation (such as 3D image processing). The graphic processing unit generates and emits more heat when executing a normal 2D image.
A conventional method of utilizing fan to cool the heat generated from a graphic processing unit, the method initials a fan when the temperature is above a predetermined temperature and turns off the fan when the temperature is below the predetermined temperature and usually the fan only turns on to cool down the graphic processing unit when the display card is on a heavy load and generating a great amount of heat. Normally, when the display card is at a light load, a heat sink or heat pipe is utilized to release the heat generated by the graphic processing unit. However, the one-step switch method causes the fan to rotate and stop within a short time. Please refer to FIG. 1. FIG. 1 illustrates a diagram of a fan switch corresponding to temperature of a conventional display card. The fan is switched on when the display card is on a heavy load and the temperature is greater than T1 (point A), after a while when the temperature drops below T1 (point B), the fan is then switched off, as the display card is still on the heavy load status the temperature quickly rises above T1 again (point C), hence the fan is overused and generating unnecessary noise from being switched on and then switched off repeatedly. Additionally, this action of repeated switching reduces the life span of the fan. Furthermore, the current cooling device of the display card in the market generally requires a software developed from the allocated hardware to control the fan rotational speed, therefore the user has to further install a fan control program included with the display card in order to manage the fan rotational speed, thus this causes inconvenience to the user.